Electric discharge lamp



July 20, 1937. J. DAVIES ELECTRIC DISCHARGE" LAMP Filed Dec. 7, 1935 INVENTOR -LEOM4/I0 J. 0/! W155 Patented July 20, 1937 UNITED STATES ELECTRIC DISCHARGE LAMP Leonard John Davies, Rugby, England, assignor to General Electric Company, a corporation of New York Application December 7, 1935, Serial No. 53,320

' In Great Britain December 12, 1934 1 Claim. (01. 176-122) This invention relates to electric discharge lamps of the kind in which the discharge is adapted to start as a glow discharge and subsequently to developintoan arc discharge having a restricted luminous column of high intrinsic brilliancy, the atmosphere within the device being provided to this end.

In lamps of this type, as the light source consists of a column of highly ionized gas at high 0 temperature, which is carrying a current of electricity, its position-can be determined by forces such as those arising from convection currents and magnetic fields. I propose to utilize this fact to produce a lamp having novel and useful characteristics.

Lamps as at present manufactured suffer from certain disadvantages; amongst which may be mentioned the necessity for a choke or inductance or resistance in series with the lamp in order to stabilize'it, owing to the arc-like or negative resistance characteristic of all known discharge lamps. A further disadvantage is that lamps of this type require, in general, a starting voltage higher than their actual operating voltage.

A lamp of the kind above set forth, according to the present invention has a low work function cathode and an anode (or two cathodes when used on alternating current), arranged in proximity to one another so as to allow the initiation of a discharge at a low voltage in an atmosphere of gas and metal vapour contained within the device, and means for creating a magnetic field located so as to deflect and lengthen the are formed during operation. The winding producing the magnetic field may be in series with the lamp or may form part of the lamp circuit with other components. The lengthening of the arc path so produced will have the effect of increasing the voltage drop across the arc, and in suitable circuits, thereby increasing the power consumed under luminous output. I further arrange the magnetic field in such a way and in such form that the ordinary negative character- 45 istic of the arc acts in such a way that the increased current that the arc takes has the eifect of increasing the length of the arcand thus increasing its voltage drop. In this manner the arc is stabilized with a much smaller value of inductance than is normally required.

The accompanying drawing illustrates the invention.

In Fig. 1, which shows a somewhat diagrammatical form of lamp for operating on alternating current, I and 2 are a pair of self-heating cathodes each consisting of a heavy filament coated with a good electron-emissive substance surrounded by an open cylindrical metal shell 3, whichcathodes are arranged closely adjacent one 60' another and supported upon leads 4 sealed into the lower end of a translucent envelope 6 which is of a glass capable of resisting attack by the metal vapour which is evolved during the opera tion of the lamp. Connected in series with the cathodes l and 2 is an inductance 'lcapableof producing during operation a magnetic field which deflects the arc upwards and lengthens it into the form somewhat as shown at 8, the bulb being designed to accommodate the extendedv are. If, during operation, the arc tends to contract the voltage drop across it diminishes, resulting in increased current flow through the inductance 1 and an increase in the magnetic field strength- This tends to lengthen the arc. By this means it will be appreciated that a self-stabilizing operation is obtained.

In an alternative form of lamp shown in Fig. 2, the two cathodes l and 2, situated with only a small gap between them which may be in the neighbourhood of one inch are arranged atthe top of the pear-shaped envelope 6. The envelope 6 is enclosed in an outer heat conserving translucent jacket 9, the space between which and the envelope 6 is preferably evacuated or may be filled with oxygen. The inductance I is located in a cap Ill cemented to the top of the outer heat conserving jacket 9. Convection currents tend to cause the arc to lengthen its path by attempting to extend upwards. -In some cases this may tend to break the arc. This tendency is opposed by the magnetic field due to induction 1 so arranged that it tends to force the are downwards andthe strength of the field is so arranged that the arc takes the form of a U. The magnetic field may be connected in series or otherwise with the are so that the arc and field tend to become self-stabilizing, in that any increase of current in the arc tends to lengthen the arc and increase its voltage drop, thus resisting the tendency for the current to increase.

What I claim as new and desire to secure by Letters Patent in the United States is:-

An electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere, a pair of closely spaced electrodes within said device, said envelope having a spheria cal portion extending away from said electrodes in one direction, at least one of said electrodes being a thermionic cathode and a magnet conheated in series with the discharge within said device, said magnet being so disposed with re- LEONARD JOHN DAVIES. 

